Viscosity sensor



No1/.26, 1963 L BUCALQ 3,111,833

' VISCOSITY SENSOR Fied July 18, 1960 2 Sheets-Sheet 1 REF. yINFUT n l 56 54` 52, FIG'. 1 I9 '7 r.{| sr-zvo REF. :i I.' 2 I8 AMP. coMP.

IN V EN TOR. LOU\S BUCALO BY FIG. 4 f a,

ATTO lNEYS Nov. 26, 1963 L. BucALo 3,111,838

vISCosITY SENSORy Filed July 1s, 1960 2 Smets-sheet 2 DIFFERENTIAL AMPLIFIER 97 96 l VENToR. F|G. 9 aucALo ATIOR United States Patent O 3,lli1,838 VISCSEY SENSOR Q Louis Rurale, Halesite, NPY., assigner to The Kinernotive Corp., a corporation of New York Filed .iuly 18, 1968, Ser. No. 43,584 i4 Claims. (Cl. 73--54) This invention relates generally to viscosity sensing systems and specifically to a viscosimeter wherein a iiuid is subjected to the action of two relatively oppositely moving surfaces, and wherein fluid pressure is measured at known positions relative to the surfaces to provide a pressure differential which serves as anindex of the viscosity of the fluid.

As is often the case, it is extremely valuable to be able to measure the viscosity of vfluids as they are transported during commercial processes. Viscosity may be affected by changes, for example, in percent concentration, in the properties of the incoming ingredients in a continuous ow process, by temperature changes, by impurities in the fluid and by losses due to evaporation or sublimation.

Viscosity (a) may be defined as the ratio of shear stress in a fluid to the rate of deformation thereof and is constant for a Newtonian fluid. `in the past, viscosity has been measured by fiow values in tubes, by torque measurements based on the Petroff equation, by comparator systems related to a uid of known viscosity and by the use of shear oats.

in order to be a satisfactory measuring tool in commercial use, as contrasted with laboratory use, a viscosirneter should function satisfactorily under the following conditions:

(a) High temperature and pressure (b) Continuous monitoring of a tank or pipeline (c) Wide ranges in different kinds of fluid tested The present invention satisfies the foregoing criteria by providing a viscosimeter which may, for example, be installed at some convenient location within a system ernploying a fluid whose viscosity is to be sensed. Advantageously, the viscosity of the fluid will be indicated in terms of a pressure differential across a body of fluid which has been subjected to certain precise mechanical shear stresses and has thus suffered commensurate deformation. This ratio of stress relative to deformation may be evaluated in terms of the static pressure of the fluid at two relatively separated stations the pressure differential thereof serving as an accurate indicator of the viscosity of the fluid.

More specifically, it is a purpose of the present invention to disclose a device characterized in that a rotor member is driven within a chamber which contains fluid Whose viscosity is to be sensed. ln one form of the device herein disclosed, the rotor has a generally frustoconical longitudinal section and is supported at a known clearance from the walls of a correspondingly shaped chamber. The axes of the rotor and the chamber are displaced a known distance such that the surface of the rotor will be eccentric relative to the walls of the chamber. Two pressure sensingT ports are defined by the chamber wall which communicate `with sensing passages connected to a diiferntial pressure sensing means. When the rotor is driven at a constant speed, a pressure differential will exist respecting the pressure sensed at ports. This pressure differential is precisely related to the degree of eccentricity of the rotor within the chamber, the speed of rotation of the rotor and the viscosity of the fluid. If all factors excepting the differential pressure and viscosity are maintained constant, changes in viscosity may be measured by the Ichanges in the differential pressure. The arrangement has the further advantage that since the rice property of differential pressure is sensed, system pressure changes will not materially affect the value of differential pressure.

Variations of the above will be disclosed Awherein means are provided for adjustably changing the eccentricity of the rotor relative to the chamber in which it is driven. ln another embodiment means are shown for varying amounts of clearance between the rotor and the adjacent chamber walls.

In a further modification according to the invention, the pressure differential in the test chamber is sensed by permitting the walls thereof to be movable in response to different pressures of the fluid acting upon them. The movement of the walls of the chamber is measured to reflect differential pressure within the chamber. The latter structure may be utilized to provide a measurement of dilferential pressure where it is inconvenient or otherwise impractical to sense pressure by means of pressure sensing ports,

rfhese and other aspects of the invention will become more lreadily apparent upon a detailed examination of the following description and of the accompanying drawing in which:

PEG. l is an illustration in cross-section of a viscosimeter constructed according to the invention which includes means for varying the effective clearance between the journal and the adjacent walls of the sensing chamber;

FEG. 2 is a cross-sectional view taken along the lines 2 2 of FIG. l;

FIG. 3 is a cross-sectional View taken along the lines 3 3 of FIG. l;

FiGS. 4 and 5 are cross-sectional views of an alternative embodiment wherein means are provided for effecting changes in the eccentricity of the ro-tor member relative to the chamber in which it rotates;

FIGS. 6 and 7 show another embodiment of the invention having separate members displacable according to pressures sensed within the chamber;

PEG. 8 is a schematic showing of the theoretical basis underlying the `structural arrangements disclosed the-rein;

FIG. 9 discloses a modification having a spherical chamber and spherical rotor element; and

FIG. 1*() illustrates the use of a single pressure port within the sensing chamber.

Referring now to the drawing and initially to FIGS. 1 3, reference numeral l@ represents the wall of a conduit or pipe adapted to transport a fluid 1l. For various reasons, it is desired to be able to provide `a continuous measurement of the viscosity of the fluid 1i as it flows through the conduit. Accordingly, the 'wall of the conduit has been provided with an aperture 12 for receiving internally of the conduit a portion of a viscosimeter 14. The viscosimeter comprises a generally cylindrical housing i6 having a radially enlarged base flange 17 which fits against the exterior of the conduit wall l@ and is attached thereto by means of bolts i8. A fluid seal is maintained between the flange il7 andthe wall lo by some suitable means such as a gasket 19.

The viscosimeter housing i6 defines a generally cylindrical enclosure Ztl having a restricted inlet opening 21 of frusto-conical design. Annular ring member 22 is located within the enclosure 26 for longitudinal siiding movement therein. The outer diameter of ring member 22 conforms closely to the inside diameter of the enclosure 29 and has an inside `surface 23 of frusto-conical design. A rotor member 24 is lsupported Within the enclosure 26' generally adjacent to the surface 23 of the annular ring member 22. The rotor 24 is provided with an outer surface Z6 which proportionally matches the frustoconical surface 23 of the ring member 22. The rotor 24 is attached to a shaft 27 supported in a sealed bearing 2S mounted in the housing l5. The shaft 27 is in driving aliases connection with a constant speed motor 29 adapted to be energized by means of the electrical connection 3%).

Adjacent the inlet 2l, the rotor 24 is provided with an acutely conical section 331. The housing 16 is formed parallel to the conical section 3l, thus defining a restricted annular passageway 32. The arrangement is such that when the rotor member 24 is driven by the motor 29, a sampling of the fluid ll. will be drawn into the inlet 2l and through the passageway 32 into enclosure Ztl. The conical section 31 and the `frusto-conical surface 26 of the rotor 24 act as a centrifugal pump, the fluid tending to be drawn toward portions of the rotor of increasing dirameter. As best seen in FG. 3, the end of the enclosure Ztl opposite to the inlet orifice 2l has been provided with a plurality of radial outlet passages 33 which permit the discharge of fluid from the enclosure Ztl. Thus, the rotor acts as a pump to provide a continuous flow of test fluid from the conduit through the viscosimeter.

As will be seen in FIG. 2, the axis of the rotor 24 is offset a distance e from the axis of the cylindrical enclosure as measured along a diameter of the latter. This causes the fiusto-conical surface 26 of (the rotor to be eccentric with respect to the adjacent surface 23 of the annular ring member 22. rPhe frusto-conical surfaces 23 and 26 of the ring member 22 and the rotor 24 respectively dene a sensing chamber 35 lying intermediate the relatively Imovable surfaces. -lt has been determined that when the rotor member 24 is rotated in a counterclockwise direction, for example, at a constant speed, a fluid intermediate the relatively rotating surfaces 23, 26 is subjected to shear stresses because of its viscosity, which produces differences in fluid pressure at separate points Within the chamber 35. If a pressure differential is taken by comparing any two pressures taken at known stations within the chamber 35, there will be provided an accurate index of the viscosity of the fluid.

With specific reference to FIG. 8, it can be shown that the pressure P at any location in the fluid contained in the chamber 35 upon a rotation being imparted by the motor 29 to the rotor 24, is:

However, for the conditions described, D, C, N and h are constant, then wld f=K^P or: Viscosityza constant times the pressure differential sensed between stations In accordance wtih the foregoing formula, two fluid pressures sensing ports 36, 37 lare located in the annular ring member 22 at diametrically vertically opposed positions respective of the longitudinal axis of fthe chamber 35 and perpendicular to a horizontal diameter which includes the eccentricity e (see FIG. 2). The ports may be located elsewhere but these locations maximize the desired output. The ports connect with passageways 36', 37 which interconnect with two spotfaces or counter-sinks 33, 39 defined within the housing 16. The housing is provided with upper and lower sensing passages 4t), 40' for the transmission of the pressure sensed within the chamber 35 respectively at the ports 36, 37. A temperature probe 42 connected to a transducer 43 is provided so that any change in viscosity due to increased temperature which is caused by the agitation of the fluid within the viscosimeter may be interpreted relative to the average temperature of the fluid in the conduit as sensed by a second reference temperature probe 42' and the transducer 43. As indicated, more or less diagrammatically, the respective pressures in the lines 4f), 40' and the output of the temperature transducers 43, 43 will be transmitted to a differential amplifier 41 for comparison. The output from the amplifier 4l may, if desired, be taken as a reading upon a gage 42a in terms of differential pressure or directly as a reading in viscosity.

-It may be desirable at times depending upon ithe characteristic of the fluids being tested or to change the sensitivity of the viscosirneter, to vary the clearance (f'=Db-D; see FIG. S) between the surfaces 26, 23 of the rotor and the annular ring member which surrounds the rotor. This may be done without varying the eccentricity e, by causing the annular ring member 22 to translate inwardly longitudinally of the rotor 24. This change in clearance C will cause changes in the differential pressure of the fluid sensed at ports 36, 37 because the fluid will be subjected to greater or less shear stress depending on the clearance C.

One means for causing such relative movement of the members has lbeen disclosed in FIG. l comprising a threaded shaft 44 which may be turned by a thumb screw 45 mounted externally of the conduit 10. The inner end of the shaft 44 is attached to an ear 46 integrally formed as a part of the ring member 22. The member 22 is mounted as previously mentioned within the cylindrical enclosure 26 for limited slidable longitudinal movement. The extent of the forward movement thereof is determined by an abutment 47 formed `by a forward portion of the housing i6, movement toward the rear being limited by an abutment 4S. Thus, the fluid within the chamber 35 intermediate the surfaces 26, 23, of the rotor and the ring member 22 may be subjected to more or less clearance between the relatively rotatable surfaces, .and thus more or less stress when the rotor member is driven. Differences in clearance effectively change the pressures sensed at the ports 36, 37, and also differential pressure according to the mathematical formula previously set forth. Of course, the rotation of the shaft 44 may be easily calibrated with respect to the clearance c between the rotor 24 and ring member 22 so the changes in differential pressure `due to changes in C may be accurately related to readings of the viscosity of the fluid being tested. `It will be noted that the translation of the annular member 22 will not displace the interconnection of the ports 36, 37 with the sensing passages 49, 40 since spotfaces 38, 39 have been provided to accommodate longitudinal shifting of the ports relative to the sensing passages.

The means for longitudinally adusting the ring member 22 may be employed in a system employing feedback to maintain a constant differential pressure output regardless of changes in the viscosity of a fluid or of different fluids. The system utilizes the `scr-called null principle where reference is made to a standard differential pressure, departures therefrom in sensed differential pressure causing energization of a means to make the sensed differential pressure equal to the reference diderential pressure.

Accordingly, the embodiment of FIGS. l-3 may be modified by employing a reference comparator 5u which senses the output differential of the differential amplifier il and compares this output to a reference input 52 provided by means such as a potentiometer 53. The reference comparator `Sti will, if a differential from the reference input standard is detected, send a signal to a servo amplifier- 54 which is adapted to energize a small reversible electric servo motor 56. The motor S5 is mechanically connected to the shaft 44 which adjusts the position of ring member 2.2 and thus, 'controls the clearance c, between the ring member and the rotor 24. The output signal from the comparator Sti will be such that the motor 5o will cause the ring member 22 to move to a position where the differential pressure sensed by the amplifier 4l no longer varies from the selected standard.

In the emobdiment of FIGS. 4 and 5, a viscosimeter 6ft is shown which is generally similar in construction to the embodiment of FIGS. 1 3; and consequently, attention will be .drawn only to those portions which differ in construction from the foregoing embodiment. The viscosimeter 6@ has a housing nl supporting an annular ring member 62 which eccentrically surrounds a rot-or 64, both the ring and rotor members being of generally frusto-conical longitudinal section. However, the ring member e2 in the embodiment is not longitudinally slidable relative to the rotor 64 but rather, may be moved transversely to vary the degree of eccentricity of the rotor relative to the ring member.

One means of causing the aforementioned translation has been shown as a longitudinal rod do threadably secured within the housing 61 such that rotation thereof will cause graduated inward or outward movement in a longitudinal direction. The end of the rod do defines a conical cam surface 67 which is adapted Ito engage the end of a transversely slidable push rod 68 afiixed to the ring member d2. rtherefore, when the rod 66 is rotated by means of a thumb screw 70, the transverse rod d8 and thus, the ring member 62 will be shifted transversely within `the viscosimeter housing. A return spring 7l has been provided intermediate the ring member 62 and the housing 6l in opposed relation to the conical camming surface 67 and the push rod 68. The spring 71 will be of sufhcients strength not to be affected by pressure from Within the rotor chamber acting thereagainst. Consequently, the rotation of the rod 66 will provide an accurate indication of the transverse position of the ring member `62 relative to the axis of the rotor and thus, an accurate index of the displacement factor e.

It will be yobserved with reference to FIG. S that two oppositely disposed pressure sensing passages 73, 73 connected to sensing ports 74, 74 have been provided perpendicular to the transverse direction of movement of the ring member relative to the rotor. The passages 73, '73 in the ring member 62 communicate with respective spotfaces 76, 76 in the housing 61 `for accommodating the relative movement of the ring member 62 relative to the housing 16. Sensing passages 77, 77 communicate with the spotfaces 76, 76 and thence to the exterior of the housing. The sensing passages may be connected to known means such las has been shown in FIG. 1, for providing a measurement of differential pressure and hence, the viscosity of the fluid in the conduit. It will be appreciated by persons skilled in the art that the feedback system described and illustrated in connection with FIG. 1 may also be employed together' with the embodiment of FIGS. 4 and 5.

FIGS. 6 and 7 illustrate a somewhat different method of employing the principles previously set forth, wherein a viscosimeter Si) is illustrated. The viscosimeter 80' has a housing 3l which defines a cylindrical enclosure S2 in which a cylindrical ring member 83 is located to encompass a cylindrical rotor S4. As best seen in FIG. 7, the ring member comprises two hollow semi-cylindrical shells S6, #86' interconnected at abutting ends by an expansible means such as the bellows S7, 87.

The semi-cylindrical halves 3.6, 86 are displ-acable radially against a resilient counterforce produced by springs 8de, fida. The halves S6, 86' are of generally light-weight construction such that fluid pressure from within a chamber 33 intermediate the members 36, S6 and the rotor 8d, acting upon the separate opposing walls of the members 36, `86 will cause them to be transversely or radially displacable relative to each other. The tendency for the upper member S6, for example to be displaced by local fluid pressure within the upper portion of the chamber S3 can `thus be compared with the tendency for the lower member 86 to be displaced by a different fluid pressure acting thereagainst (as will be produced by rotation of the rotor 34) to provide a measurement of di. erential pressure within the chamber. As illustrated, the differential movement of the semi-cylindrical halves Se, Se may be sensed by an appropriate means such `as strain gages 85, 81S', for example and transmitted to a dilferential amplifier S9' whose output may be read upon a gage 89a associated therewith in terms of fiuid viscosity. llt is contemplated that the embodiment of FIGS. 6 and 7 will be especially useful Where the viscosity of the fluid being tested is extremely great such that the measuring of pressure by sensing ports within the chamber 83 would be subect to inaccuracies.

In FIG. 9 a viscosimeter 9d is shown which has a housing QI defining a spherical test chamber 92 intermediate the housing and a spherical rotor '94. The viscosimeter 9? has been provided with inlet means 9S and outlet means 96 to and from the chamber 92 and sensing passages $7, 97 connecting with the chamber 192 according to the principles illustrated previously. Some pumping action will be present due to the spherical shape of the rotor 94, however, it is thought that the embodiment of FIG. 9 will not be used as an on-stream device such as in the previous embodiments, but rather, for testing the viscosity of fluids in open containers and the like. The visconsimeter 9d is portable having a handle 913 that may be held While the inlet end thereof is dipped into a vat holding a test Huid. Of course, any of the previously discussed embodiments may be made portable and may serve in a similar manner.

FIG. if) illustrates a modification of the invention utilizing structure similar to that shown in FIG. 5. In the embodiment of FIG. l0, only one sensing-port 1061 has been provided within the test chamber defined by a rotor itil and the annular ring member I162. A second port M93 is located in the housing of the viscosimeter in a position to sense system pressure or P0. The respective pressures sensed by the ports 10d and 103 will be reflected within the sensing passages 104, IGS and therefrom to a differential amplifier 1%. As in the earlier embodiments, the differential pressure will provide an indication of the viscosity of `the fluid, the latter value being read upon the gage 167. Since the differential pressure sensed by the embodiment of FIG. 10 includes system pressure or P0 the differential pressure sensed will vary with changes in P0 which Would not be the case for the dual port systems of the preceding specific embodiments.

It will be apparent that the fore-going description relates to specific embodiments and is merely representative. Various changes may be made therefrom without departing from the teachings of the invention. For example, although a single rotor member has been disclosed, which is driven relative to the Wall of a surrounding chamber, itis obvious that the rotor element may remain stationary and the outer wall of the chamber driven relative thereto. Or both may be driven in counter rotation. It is equally "7 true that it is not absolutely necessary to drive the rotor at a constant speed. Provided that suitable calibrations of differing rotor speeds is made, the rotor speed may be varied to increase or decrease the sensitivity of the device, with higher rotor speeds producing greater amplification of t'he pressure differential which will be sensed when testing a given huid.

yFurtlfie-r, those skilled in the art will appreciate that the sensing of pressures within a fluid subjected to internal shear stresses, and the taking of a diierential pressure reading thereof, `may be measured in several ways other than those disclosed specifically in connection with the particular embodiments described above. These have indicated that a pressure differential within the test chamber (i.e., the chamber defined by the rotor and the surrounding portions of the housing) may be sensed by the use of two separated pressure ports within the test chamber or by sensing the movement of relatively movable parts of the housing which deiine the chamber. As in FIG. l it is also possible to .have only one port within the test chamber, which will then provide a pressure reading relative to system pressure or P0.

Where the two ports are provided within the test chamber, they need not necessarily be located in the same transverse plane, as has been illustrated. The optimum location will normally be at at a position intermediate the length of the rotor; however two ports may Ibe situated in line relative to the longitudinal axis of the test chamber, or two pains of ports may be so aligned. With suitable calibration, two sensing ports may be longitudinally disposed and misaligned. These various alternate locations have been proposed merely to show that the teaching of the present disclosure is sufficiently broad to encompass the above generally equivalent means for measuring viscosity. l

Thus, the several forms of the present invention each possesses the advantage of providing an indication of viscosity by measuring the pressure of a iluid which has been subjected to internal shear stresses. The term l'luid has 'been used purposefully throughout the present disclosure since it is obvious that the invention has application to the measuring of the viscosity of gases as well as liquids. The advantage of pressure measurement over torque sensitive measurements of viscosity for example, is that bearing torque or torque effects produced by lluid sealing elements does not have to Ibe calibrated out in order to obtain true viscosity readings.

Since changes may be made from what has been speciiically shown and described without departing from the teachings of the invention, in order to appreciate fully the spirit and scope of the present invention, reference should be made to the appended claims, in which l claim:

l. A viscosity sensor comprising a housing deiining a chamber having a transverse circular cross-section, a rotor having a transverse circular cross-section mounted within said chamber, the longitudinal axis of said rotor being parallel to the longitudinal axis of said chamber and displaced therefrom a predetermined distance to provide an eccentricity between the surface of said rotor and the interior surface or" said housing, the diameters of said rotor and said chamber defining a predetermined varying clearance extending continuously between the periphery of said rotor and the interior surface of said housing, means for 'driving said rotor at a predetermined speed, inlet means to said chamber for admitting lluid thereto and pressure sensing lmeans for sensing different pressures of the fluid within separate circumferentially displaced portions of said chamber respective of the interior sui"- face of said housing and intermediate the rotor and housing deining said clearance, and means for registering a differential of said diilerent sensed pressures to provide an indication of the viscosity of the lluid when said rotor is driven in said chamber.

2. A viscosity sensor according to claim l in which said pressure sensing means includes sensing ports deiined by the wail of said chamber and sensing passages connected to said ports.

3. A viscosity sensor accord-ing to claim 2 in which said chamber and said rotor are defined at least in part by members having generally parallel longitudinal frustoconical cross-sections, said inlet means being located adjacent said rotor at .a minimum diameter thereof and outlet means from said chamber being provided adjacent a maximum diameter of said rotor.

4. A viscosity sensor according to claim 3 in which the member' deiining said chamber is an annular ring adjustably movable within said housing in a longitudinal direction to vary the clearance between said rotor and said chamber and means are provided for causing the longitudinal adjustment of said ring.

y5. A viscosity sensor according to claim 4 which includes means for adjusting the annular ring relative to the periphery of said rotor to maintain the sensed differential pressure equal to a selected reference diierential pressure, said last-mentioned means comprising means associated with said sensing passages for measuring differential pressure and for providing an output in accordance with sensed differential pressure, means for receiving said sensed differential pressure and for comparing the value thereof with a selected reference differential pressure, said comparing means being used to actuate a means for adjusting said annular ring relative to the periphery of said rotor by a predetermined extent in a direction to maintain the sensed differential pressure equal to the selected reference diilerential pressure.

6. A viscosity sensor according to olaim 3 in which the mein-ber defining said chamber is movable transversely of the axis of the rotor to vary the displacement of said axis relative to the axis of said chamber.

7. A viscosity sensor according to claim 2 in which said chamber and rotor are spherical in shape.

8. A viscosity sensor according to claim l in which said chamber is defined by members transversely displaceable relative to each other in response to diilerences in pressure within said chamber reacting upon said members.

9. A viscosity sensor according to claim 7 in which said members form opposing portions of a ge erally cylindrical chamber, said portions being connected by an expansible bellows, and `being connected to a sensing means for determining the relative displacement of each of said portions with respect to the other.

l0. A viscosity sensor comprising a housing, a portion of which is adapted to be received within an aperture in the wall of a conduit carrying a fluid whose viscosity is to tbe measured, a base `flange on said housing for attachment to exterior portions of the wall of said conduit adjacent said aperture, means for maintaining a lluid-tight seal between said base. and said conduit, said housing defining a chamber for the admission of iluid from said conduit, said chamber having a frusto-conical longitudinal section and inlet means communicating adjacent the portion of least diameter of said truste-conical section, a rotor having a major surface of generally frusto-conical longitudinal section disposed in said chamber with the axis thereof generally parallel to the axis of said chamber and displaced therefrom a predetermined distance to provide an eccentricity between the surfaces of said rotor and said housing, said chamber' and sai-d rotor having a known varying clearance therebetween continuously extending between the adjacent sur-faces of said rotor and housing, said rotor also having a second surface of longitudinal conical section lforming the apex thereof adjacent the inlet to said chamber, rneans for driving said rotor at a predetermined speed and outlet means removed from said inlet means for exhausting fluid from said chamber to said conduit, and said chamber defining sensing ports communicating with sensing passages for providing a measurement of different fluid pressures intermediate adjacent eccentrically positioned surfaces of said rotor and housing in said chamber at separate positions therein displaced circumerentially with respect to the interior surface of said housing.

11. A viscosity sensor according to claim wherein said inlet to said chamber is of frusto-conical longitudinal section decreasing in diameter toward the apex of said rotor.

12. A viscosity sensor comprising a housing defining a chamber having a transverse circular cross-section, a member having a transverse circular cross-section mounted Within said chamber, the llongitudinal axis of said member Ibeing parallel to the longitudinal axis of said chamber and dis-placed therefrom a predetermined distance to provide an eccentricity between the surfaces of said member and housing, the diameters of said member and said chamber deiining a predetermined varying clearance about the periphery of said member extending continuously between the adjacent surfaces of said mem ber and housing, driving means for causing relative rotation between said housing and said member at a predetermined speed, inlet means to said chamber for admitting fluid thereto and Ipressure sensing means for sensing a difference in .pressure of the fluid at separate stations caused by said eccentricity, at |least one station being intermediate the adjacent eccentrically positioned surfaces of said member and housing, and means for comparing 10 a differential of said sensed pressures to provide an indication oi the viscosity of the tluid when said housing and said member are driven in relative rotation.

13. A viscosity sensor according to claim 12 wherein a single Huid press-ure port is located Within said chamber and a second uid pressure port is situated in a position to sense iiuid pressure externally of said chamber and means are provided for registering a differential of said sensed pressures to provide yan indication of the viscosity of the uid.

14. A viscosity sensor according'to claim 1 in which the press-ure sensing means are at generally diametrically opposed positions and generally at positions perpendicular to a diameter of said chamber which includes a minimum `and maximum clearance produced Iby said eccentricity.

References Cited in the le of this patent UNITED STATES PATENTS 2,027,903 Dintilhac Jan. 14, 1936 2,198,325 IWynn et al Apr. 23, 1940 2,869,358 Heisig Jan. 20, 1959 2,977,790 Dubsky et al. Apr. 4, 1961 FOREIGN PATENTS 539,751 {France June 30, 1922 OTHER REFERENCES Rich: abstract of application Serial Number 151,142, published Nov. 18, 1952, 664 O.G. 9601. 

1. A VISCOSITY SENSOR COMPRISING A HOUSING DEFINING A CHAMBER HAVING A TRANSVERSE CIRCULAR CROSS-SECTION, A ROTOR HAVING A TRANSVERSE CIRCULAR CROSS-SECTION MOUNTED WITHIN SAID CHAMBER, THE LONGITUDINAL AXIS OF SAID ROTOR BEING PARALLEL TO THE LONGITUDINAL AXIS OF SAID CHAMBER AND DISPLACED THEREFROM A PREDETERMINED DISTANCE TO PROVIDE AN ECCENTRICITY BETWEEN THE SURFACE OF SAID ROTOR AND THE INTERIOR SURFACE OF SAID HOUSING, THE DIAMETERS OF SAID ROTOR AND SAID CHAMBER DEFINING A PREDETERMINED VARYING CLEARANCE EXTENDING CONTINUOUSLY BETWEEN THE PERIPHERY OF SAID ROTOR AND THE INTERIOR SURFACE OF SAID HOUSING, MEANS FOR DRIVING SAID ROTOR AT A PREDETERMINED SPEED, INLET MEANS TO SAID CHAMBER FOR ADMITTING FLUID THERETO AND PRESSURE SENSING MEANS FOR SENSING DIFFERENT PRESSURES OF THE FLUID WITHIN SEPARATE CIRCUMFERENTIALLY DISPLACED PORTIONS OF SAID CHAMBER RESPECTIVE OF THE INTERIOR SURFACE OF SAID HOUSING AND INTERMEDIATE THE ROTOR AND HOUSING DEFINING SAID CLEARANCE, AND MEANS FOR REGISTERING A DIFFERENTIAL OF SAID DIFFERENT SENSED PRESSURES TO PROVIDE AN INDICATION OF THE VISCOSITY OF THE FLUID WHEN SAID ROTOR IS DRIVEN IN SAID CHAMBER. 